LED lighting is increasingly popular due for example to its relatively long life, better lumen output per watt than alternative lighting techniques, and superior dimming capability. Traditional LED drivers lack inherent capability to report individual driver power consumption information to the customer. However, it is very desirable for a customer to have this information to better manage the power consumption in a given facility.
In a typical AC power distributing system, the average power is defined by:
                              P          average                =                              1            T                    ·                                    ∫              0              T                        ⁢                                                            v                  ⁡                                      (                    t                    )                                                  ·                                  i                  ⁡                                      (                    t                    )                                                              ⁢                                                          ⁢              d              ⁢                                                          ⁢              t                                                          (        1        )            
If a current has a phase shift a with respect to the voltage, then the average active power can be calculated as:
            1              2        ·                  π          w                      ·                  ∫        0                  2          ·                      π            w                              ⁢                                    v                          r              ⁢                                                          ⁢              m              ⁢                                                          ⁢              s                                ·                      2                    ·                      cos            ⁡                          (                              w                ·                t                            )                                ·                      I                          r              ⁢                                                          ⁢              m              ⁢                                                          ⁢              s                                ·                      2                    ·                      cos            ⁡                          (                                                w                  ·                  t                                -                a                            )                                      ⁢        d        ⁢                                  ⁢        t              →            I              r        ⁢                                  ⁢        m        ⁢                                  ⁢        s              ·          V              r        ⁢                                  ⁢        m        ⁢                                  ⁢        s              ·          cos      ⁡              (        a        )            
which simplifies to:P_average=Irms·Vrms·cos(a)  (2)with Irms being the RMS input current and Vrms being the RMS input voltage.
Most of the time utility companies only charge customers for active power or average power. From equation (2) we see that we need to know the RMS input current Irms, the RMS input voltage Vrms, and the phase shift a to accurately calculate active input power. Unfortunately, it is exceedingly costly to implement circuitry designed to accurately measure those three necessary variables.